Wells drilled in low-permeability subterranean formations are often treated by reservoir stimulation techniques, such as hydraulic fracturing, to increase their conductivity and thereby enhance recovery of hydrocarbons. Treatment fluids are pumped at high pressure into the formation to create fractures in the formation. Proppants may be incorporated in the fluids to prop open the created fractures when the surface treating pressure is released. Hydrated polymers by themselves generally do not possess enough viscosity for proppant transport at temperatures encountered in the well. Thus, additional viscosity may be generated by crosslinking the polymers with crosslinkers, such as boron, zirconium, and titanium compounds. Examples of polymers known for use in reservoir stimulation include polysaccharides, such as guar gum or its derivatives, and cellulose derivatives. Derivatized guar and cellulose include carboxymethyl guar (CMG), hydroxypropyl guar (HPG), carboxymethylhydroxypropyl guar (CMHPG), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), and carboxymethylhydroxyethyl cellulose (CMHEC).
Research and development has included finding viable alternatives to guar gum. Derivatized cellulose such as CMC, HEC, and CMHEC was identified as a guar alternative. One benefit of CMC, HEC and CMHEC is that they contain fewer insoluble residues, therefore, they are cleaner polymers and less damaging to the subterranean formation than guar-based polymers. CMC is less expensive than double derivatized CMHEC, both of which may crosslink at a low pH, such as no more than about 6.8, using crosslinkers with transition metals, such as zirconium. One disadvantage of known low pH crosslinking fracturing fluid based on CMG, CMHPG, CMC, or CMHEC is rapid or non-delayed viscosity development, which generates pipe friction pressure during pumping and results in mechanical shearing of the fluid. Accordingly, fluids with other viscosity development characteristics are desirable.